NRE, or falling in love, is not really the most intelligent reactions out there. It's a hormone overdose, and hormones are not that picky.
Ever tried to help a dog who is hurting, or tried to separate two dogs fighting? The cutest and most loving family dog ever might bite their owner, not because they want to attack them, but because if somebody touches them while they are hurting, their brain makes the connection 'hurt-touch-the toucher is hurting me', and they lash out.
So when you are walking around, all soaked up in hormones, and your established partner touches you, your brains make the same connection. It's like booze; ethanol doesn't really make you more sociable, but makes you more reactive to the moods around you. So if you are drunk at a party where people are having a good time, you start feeling good. If you are drunk home alone and watching weepy films, you start feeling lonely.
Me: bi female in my twenties